Nikolai G. Lehtinen, Timothy F. Bell, Umran S. Inan and Jonah J. Colman
STAR Laboratory, Stanford, CA 94305
Koç University, Rumelifeneri Yolu, 34450 Sariyer, Istanbul, Turkey
Air Force Research Laboratory, Space Vehicles Directorate, 3550 Aberdeen Ave., S.E., Kirtland AFB, NM 87117-5776
VLF radiation from lightning
We apply the Stanford FWM (full-wave method) to calculate the electromagnetic radiation from lightning, both into the Earth-ionosphere waveguide and into the ionosphere. The calculated sferic waveforms (i.e, the waveguide radiation) are validated against observed waveforms. The radiated energy spectrum and its apportionment between the waveguide and ionosphere strongly depend on the frequency at which the radiation is observed, due to different efficiencies of the excitation of waveguide eigenmodes. The radiated waves also strongly depend on the wave propagation environment and the source characteristics. The wave propagation environment includes, e.g., the ionosphere profile and the direction of the geomagnetic field. The source is characterized by its location and orientation, which may be used to distinguish the effects of the cloud-to-ground or intracloud lightning. The recently discovered [Starks et al., 2008] deficit of VLF transmitter power observed by satellites, caused by scattering of VLF waves on ionospheric irregularities and the transfer of energy into quasi-electrostatic whisler-mode waves, may lead to a similar modification of lightning radiation in the ionosphere and have effects on the global lightning VLF energy input into the ionosphere.